IWbemHiPerfProvider::QueryInstances method (wbemprov.h)

The IWbemHiPerfProvider::QueryInstances method returns instances of the specified class using the supplied IWbemObjectSink instance. The method should return immediately. The IWbemObjectSink interface is used to specify results.

Syntax

HRESULT QueryInstances(
  [in] IWbemServices   *pNamespace,
  [in] WCHAR           *wszClass,
  [in] long            lFlags,
  [in] IWbemContext    *pCtx,
  [in] IWbemObjectSink *pSink
);

Parameters

[in] pNamespace

An IWbemServices pointer back to WMI that can service any request from the provider. The provider should call AddRef on this pointer if it needs to call back to WMI during execution.

[in] wszClass

Pointer to a WCHAR string that specifies the class whose instances are returned.

[in] lFlags

Integer that contains the flags.

[in] pCtx

Typically NULL; otherwise, a pointer to an IWbemContext object that is required by one or more dynamic class providers. The values in the context object must be specified in the provider documentation. For more information, see Making Calls to WMI.

[in] pSink

Pointer to the IWbemObjectSink implementation that is provided by the client to any of the asynchronous methods of IWbemServices.

Return value

This method returns an HRESULT that indicates the status of the method call. The following list lists the value contained within an HRESULT.

HiPerf providers can report success or failure either through the return code from QueryInstances or through a call to the SetStatus method of pResponseHandler. If you call the SetStatus method, the return code sent through pResponseHandler takes precedence over the QueryInstances return code.

Remarks

WMI calls QueryInstances in response to an IWbemServices::CreateInstanceEnum or IWbemServices::CreateInstanceEnumAsync request.

The IWbemObjectSink::SetStatus method is called to indicate the end of the result set. When error conditions occur, IWbemObjectSink::SetStatus may also be called with no intervening calls to IWbemObjectSink::Indicate.

Examples

The following code example shows how to implement QueryInstances.

HRESULT CMyHiPerfProvider::QueryInstances(
    /* [in] */ IWbemServices* pNamespace,  
    /* [in] */ BSTR strClass,
    /* [in] */ long lFlags,
    /* [in] */ IWbemContext __RPC_FAR *pCtx,
    /* [in] */ IWbemObjectSink __RPC_FAR *pSink
)
{
   IWbemClassObject *pClass = 0;
   IWbemClassObject *pNextInst = 0;

   // The IWbemObjectSink interface must be
   // implemented in a class that you define. You then
   // must assign the pResponseHandler pointer
   // an instance of the class that implements
   // the IWbemObjectSink interface.
   IWbemObjectSink* pResponseHandler = 0;
   HRESULT hRes;

    // Use the namespace pointer to retrieve a class
    // definition.

   hRes = pNamespace ->GetObject(strClass, 0, NULL, &pClass, 0);
   if (WBEM_NO_ERROR==hRes)
       return hRes;


    // Now loop through the private source and create each instance.

     for (int i = 0 ; i < NUM_OF_INSTANCES ; i++)
    {
         hRes = pClass->SpawnInstance(0, &pNextInst);

         // Exit loop if no new instance is spawned
         if (WBEM_S_FALSE == hRes)
            break;

        if(NULL!=pNextInst)
       {
        // Create the instance.
        // For example, call a function (FillInst) that
        // assigns a value to the pNextInst pointer.
        /*FillInst(pNextInst);*/

        // Deliver the class to WMI.
        pResponseHandler->Indicate(1, &pNextInst);
        pNextInst->Release(); 
        pNextInst=NULL;
       }
    }

   // Send a finish message to WMI.
    pResponseHandler->SetStatus(0, WBEM_S_NO_ERROR, 0, 0);
    // Free memory resources.
    pNamespace->Release();
    pClass->Release();
    SysFreeString(strClass);

  return WBEM_S_NO_ERROR;
}

Requirements

See also

Developing a WMI Provider

IWbemHiPerfProvider

Making an Instance Provider into a High-Performance Provider

Performance Counter Provider

Writing an Instance Provider